Handpiece with a microchip laser

ABSTRACT

A microchip laser and a handpiece including the microchip laser. The microchip laser includes a laser medium with input and output facets. The input facet is coated with a highly reflective dielectric coating at microchip laser wavelength and highly transmissive at pump wavelength. The output facet is coated with a partially reflective at microchip laser wavelength dielectric coating. A saturable absorber attached by intermolecular forces to output facet of microchip laser. A handpiece for skin treatment includes the microchip laser.

CLAIM OF PRIORITY

This application is a divisional application of U.S. patent applicationSer. No. 16/015,249, filed on Jun. 22, 2018, the entire contents ofwhich are hereby incorporated by reference.

TECHNOLOGY FIELD

The present system relates to a passively Q-switched microchip laserpackaged in a handpiece and in particular to microchip lasers withdouble pass pumping configuration.

BACKGROUND

Systems for non-invasive treatment of skin disorders known in the art.Typically, such system includes a cabinet into which a laser is placedand an articulated arm connected a handpiece that conducts the laserradiation from the laser to a segment of skin to be treated. Thefunctionality of such a system is limited by the capabilities of theselected laser. Treatment of skin imperfections usually requires morethan one type of laser and frequently more than one type of laser isplaced in the cabinet. This increases size, cost and complexity of thesystem.

Treatment of some skin imperfections requires significant laser power(tens and even hundreds of MW) that in order to prevent skin damage issupplied in ultrashort femto or picosecond pulses. Such laser power isdifficult to transfer through a fiber and use of articulated armsignificantly limits the freedom of the caregiver.

Microchip lasers are alignment-free monolithic solid-state lasers wherethe active laser media is in direct contact with the end mirrors formingthe laser resonator. In many cases the mirrors, which are dielectriccoatings, are simply deposited on the end faces of the active lasermedia. Microchip lasers are usually pumped with a laser diode andtypically emit on average a few tens or hundreds milliwatts of power,although reports of microchip lasers emitting 10 W have been published.The dimensions of the microchip laser are small and support theirplacement in almost any desired place in the system.

A typical Q-switched microchip lasers consist of a laser medium and asaturable absorber as a passive Q-switcher bonded together as oneelement. Microchip lasers are small, linear cavity, monolithicsolid-state lasers with dielectrically coated cavity mirrors. Thetypical cavity length is on the order of millimeter. The short cavitylengths result in extremely short cavity lifetimes, and the possibilityof much shorter Q-switched pulses. It has been demonstrated thatQ-switched microchip lasers can produce output pulses shorter than 300ps, as short as large mode-locked lasers produce with peak powers ofabout 10 KW, similar to commercially available large Q-switched systemsproduce.

Over decades, a lot of effort has been put in places striving forgeneration of high energy picosecond lasers. Many techniques have beendeveloped. These techniques commonly involve multi-stage configurations,i.e., a low energy picosecond seed laser, for example nJ or μJ are fedinto amplification stages (including regenerative amplifier or/andmulti-pass amplifications). Such multi-stage configurations requirecomplex optical arrangement and sophisticated electronic synchronizationfurther increasing the complexity and cost of the system.[16, 17, 18,20, 25, 28]

SUMMARY

Disclosed is a microchip laser and a method to implement a handpiecewith passively Q-switched microchip laser with double pass pumpinggeometry. The laser medium and saturable absorber are sandwiched with ahighly reflective dielectric coating at pumping wavelength and bondedwith optical contact by intermolecular forces. The highly reflectivedielectric coating supports achieving double passing pumping and avoidsunwanted bleaching of passive Q-switch by unabsorbed pump laser.

The dimensions of the microchip laser support the microchip laserpackaging in a handpiece that can be used in different applications andin particular for skin disorders treatment. The handpiece is adapted tobe applied to skin and slide over the skin. The handpiece could includea scanning system configured to scan a laser beam emitted by themicrochip laser across a segment of skin. The scanning system couldprovide a one-dimensional (1-D) or a two-dimensional (2-D) treated skinarea coverage. Fractionated micro-dot line beam pattern is supported.The microchip laser handpiece could contain second or higher orderharmonic generator to generate an additional laser wavelength.

A system based on the microchip laser uses Alexandrite laser as a pumpsource. Alexandrite laser, which provides over 1 kW pumping power forhigher pulse energy generation. The high pumping power facilitatesenergy storage that is further facilitated by use of a saturableabsorber of low initial transmission. Generation of picosecond laserpulses with high peak power of about 100 MW and higher has beendemonstrated.

LIST OF FIGURES AND THEIR BRIEF DESCRIPTION

For a more complete understanding of this disclosure and its features,reference is now made to the following description, taken in conjunctionwith accompanying drawings, in which like reference numerals denote likeelements:

FIG. 1 is an example of a microchip laser;

FIG. 2 is an example illustrating the bonding of laser medium andsaturable absorber of a microchip laser;

FIG. 3 is an example of a microchip laser supporting second harmonicgeneration (SHG);

FIG. 4 is an example of a microchip laser supporting sum frequencygeneration (SFG);

FIG. 5 is an example of a microchip laser supporting fifth harmonicgeneration (FHG);

FIG. 6 is an example of a handpiece for fractional skin treatment;

FIG. 7 is an example of a sparse fractional skin treatment pattern;

FIG. 8 is an example of a denser fractional skin treatment pattern; and

FIG. 9 is another example of a handpiece for fractional skin treatment.

DESCRIPTION

The present disclosure suggest mounting of a passively Q-switchedmicrochip laser in a handpiece, thereby reducing the size and complexityof the total system and improving the power utilization efficiency. Thedisclosure also suggests a novel and more robust microchip laser. TheQ-switched microchip laser emits picosecond pulses at a laser power oftens and hundreds of MW.

The passively Q-switched microchip laser does not require switchingelectronics, thereby reducing the size and complexity of the totalsystem and improving the power efficiency. In addition, there is no needfor interferometric control of the cavity dimensions, simplifyingproduction of the device and greatly relaxing the tolerances ontemperature control during its use. The result is a potentially lessexpensive, smaller, more robust, and more reliable Q-switched lasersystem with performance comparable with that of the coupled cavityQ-switched microchip laser. With this combination of attributes,passively Q-switched picosecond microchip lasers are attractive for alarge range of applications, including high-precision ranging, roboticvision, automated production, nonlinear frequency generation,environmental monitoring, micromachining, cosmetics and microsurgery,and ionization spectroscopy as well as automobile engine ignition.

Microchip Laser

Passively Q-switched microchip lasers have been investigated extensivelyfor several decades. However, the most studies reported generation ofless than a few millijoule pulse energy and less than 10 MW peak power[1-15, 19, 21-26, 28, 29]. In particular, some of microchip lasers wereonly capable to produce nanosecond laser pulse duration [3, 4, 7, 13,23, and 24]. Most recently, X. Guo et. al demonstrated the generation of12 mJ from Yb:YAG/Cr:YAG microchip laser[1]. However, only ˜3.7 MW peakpower was achievable due to longer pulse duration (1.8 ns).

Furthermore the laser had to be operated under cryogenic condition(i.e., 77 degrees K) which makes practical application problematic. Tothe best knowledge of the inventor, the generation of >100 MWsub-nanosecond laser pulses has not been reported directly frompassively Q-switched microchip laser.

Single pass pumped microchip lasers have several limitations. In orderto ensure the sufficient absorption of pumping energy in the lasermaterial, the laser medium has to be sufficiently long, however longerlaser medium will lead to longer emitted pulse duration. In addition, atsome particular pump wavelengths, the unabsorbed pump laser can resultin unwanted bleaching of saturable absorber causing failure ofQ-switching operation. To overcome these above-mentioned issues, thepresent disclosure introduces a microchip laser with double passpumping. Double pass pumping also facilitates use of the laser mediumproduced from crystals which are difficult to be doped (i.e., Nd:YAG) orhave a weak absorption of laser medium at the available pump laserwavelength. The double pass pumping can be made possible by applyinghighly reflective dielectric coating in between the laser material andpassive Q-switch while two materials are bonded together to formmicrochip laser. The double pass pumped microchip laser supports pumplaser absorption and shorter medium length leading to shorter pulseduration as well as a more compact laser layout.

The present disclosure describes a microchip laser for producingsub-nanosecond laser pulse with high peak power exceeding 100 MW.

Microchip laser 100 is shown in FIG. 1. Microchip laser 100 includes alaser medium 104, such as for example, Nd:YAG and Nd: a highlyreflective dielectric coating 108 for pumping laser wavelengthsandwiched in between laser medium 104 and a saturable absorber 112.Also shown in FIG. 1 are Alexandrite laser pumping beam 116 andmicrochip laser 100 output beam 120. The Alexandrite laser output beam120 could be, for example a beam with ˜752 nm nm wavelength. Highlyreflective dielectric coating 108 (highly reflecting at pump laserwavelength, 752 nm and highly transmitting Q-switched laser wavelength,1064 nm)) supports achieving double passing pumping and avoids unwantedbleaching of passive Q-switch 112 by unabsorbed pump laser leakingthrough it.

An input end 124 of the microchip laser 100 (i.e., the surface of lasermaterial 104) is coated with a highly reflective at microchip laser 100wavelength e.g., 1064 nm dielectric coating and highly transmissive atpump wavelength. The output end of microchip laser 100 i.e., surface 128of passive Q-switch 112 is deposited with dielectric coating partiallyreflective at the microchip laser 100 emitted laser wavelength. Thecoating of output facet of the microchip laser considers the refractiveindices of laser medium and saturable absorber such that the coatingfunctions as required when the monolithic material is formed.

These two ends (124 and 128) are arranged to be parallel and coated withdielectric coating, allowing laser oscillation occurs.

Diffusion bonding is commonly used to bond laser material and passiveQ-switching element (i.e. saturable absorber) to form passivelyQ-switched microchip laser. This method is typically accomplished at anelevated pressure and temperature, approximately 50-70% of the absolutemelting temperature of the placed in contact materials. Such fabricationprocess involving elevated temperature and makes it difficult to depositany form of dielectric coating in between two elements (i.e., lasermedium and passive Q-switcher), in particular, highly reflective coatingat pump laser wavelength. Therefore, single pass pumping can be onlyapplied.

In the current disclosure, the bonding between laser medium 104 andsaturable absorber 112 is implemented as illustrated by arrows 204through optical contact by intermolecular forces, such as Van der Waalsforces, hydrogen bonds, and dipole-dipole interactions, as shown in FIG.2. No elevated temperature and pressure is needed so that integrity ofreflective dielectric coating 108 is protected.

The two surfaces of being contacted i.e., 208 of laser medium 104 and212 of saturable absorber 112 are processed in optical quality toachieve stable optical contact. The highly reflective dielectric coatingat an interface between laser medium 104 and saturable absorber 112 atpump wavelength supports achieving double passing pumping and avoidsunwanted bleaching of passive Q-switch by unabsorbed pump laser.Generally, the surface quality could be better than 20-10 scratch-dig.The flatness and roughness could be at least λ/4 10 A rms or better,respectively.

Microchip laser medium 100 and saturable absorber 112 could be Nd dopedcrystal (i.e., YAG or YLF or ceramic. The materials for the laser mediumand saturable absorber can be of the same host material or of differentmaterials. This is quite different from the existing microchip laserbonded through diffusion method where the material physical properties(i.e., melting point, thermal expansion coefficient, etc.) for twocomponents should be similar.

The passively Q-switched microchip laser with double pass pumping offersadvantage over that with single pass pumping by generating much shorterpulses due to the shorter laser material used. This is because of theQ-switched pulse duration is roughly proportional to the cavity length.Furthermore, for a crystal with low doping concentration or lowabsorption at pumping laser wavelength, double pass pumping makes itpossible to obtain sufficient pump laser absorption while maintainingshorter crystal length leading to a more compact laser design.

The system uses Alexandrite laser as a pump source. Alexandrite laserwhich can provide over 1 kW pumping power for higher pulse energygeneration. The high pumping power facilitates energy storage that isfurther facilitated by use of a saturable absorber of low initialtransmission. Generation of picosecond laser pulses with high peak powerof about 100 MW and higher has been demonstrated.

The high energy/high peak power ultrashort pulse microchip laserfacilitates efficient non-linear frequency conversation includingharmonic generation (second harmonic, third harmonic, fourth harmonic,sum frequency generation, OPO, etc) and super continuum generation wherethe high peak power is required. In contrast to the existing low energymicrochip laser, the high energy microchip laser can provide higherenergy/power at frequency converted wavelengths therefore significantlyincrease measurement precision by improving signal to noise ratio. Mostimportantly, the optical arrangement is very compact and simple andsupports mounting of the microchip laser in constrained space forexample, in a handpiece.

FIG. 3 is an example of a microchip laser supporting second harmonicgeneration. For generation of stable linearly polarized Q-switchedlaser, <110> cut Cr⁴+:YAG is used. A second harmonic generation crystal(SHG) 304, which could be such as lithium niobate (LiNbO3), potassiumtitanyl phosphate (KTP=KTiOPO4), and lithium triborate (LBO=LiB3O5) orany other SHG receives microchip laser 100 output beam 120 withwavelength of 1064 nm and transforms it into two beams—one beam 320maintaining the original wavelengths (frequency) of 1064 nm and a beam312 having a frequency two times higher than the original beam 120 haswith a wavelength of 532 nm. Beam splitter 308 splits and directs indifferent directions beams 320 and 312 facilitating their use.

FIG. 4 is an example of a microchip laser supporting sum frequencygeneration (SFG). Sum frequency generation (SFG) or difference frequencygeneration (DFG) can occur, where two laser pump beams generate anotherbeam with the sum or difference of the optical frequencies of the pumpbeams 312 and 320 with wavelengths of 532 nm and 1064 nm. For example,mixing the output of a 1064-nm laser beam with frequency-doubled laserbeam with 532 nm using a SFG crystal 404, would result in an outputlight beam 408 with 355-nm UV light.

FIG. 5 is an example of a microchip laser supporting fourth harmonicgeneration (FHG). The fourth harmonic generation is a process designedto produce UV-radiation for example at 266 nm or even shorterwavelengths. For example, the fourth harmonic of Nd:YAG laser producinga laser beam with wavelength of 1064 nm would be a light beam withwavelength of 266 nm. Numeral 502 marks an FHG crystal and numeral 506marks an output beam with wavelength of 266 nm.

Such frequency conversation processes can offer a wide range of spectrumwith sufficient energy for different spectroscopy application. Incontrast to the existing low energy microchip lasers, this high energymicrochip laser can provide higher energy/power at frequency convertedwavelengths therefore significantly increase measurement precision byimproving signal to noise ratio. The optical arrangement is very compactand simple.

The disclosed high peak power microchip laser producing picosecondpulses could be used in many additional to spectroscopy fields. Theseinclude skin treatment, micromachining, efficient non-linear frequencyconversation including harmonic generation (second harmonic, thirdharmonic, fourth harmonic, sum frequency generation, OPO, etc) and supercontinuum generation where the high peak power is required. Suchfrequency conversation processes can offer a wide range of spectrum withenergy for spectroscopy application.

Handpiece

One of potential and promising applications for the disclosed high peakpower microchip laser producing picosecond laser pulses would be incosmetic and medical laser systems. The high energy short pulsemicrochip laser supports packaging of the microchip laser into ahandpiece to perform meaningful aesthetic treatment and in particularfractional skin rejuvenation. It has been demonstrated clinically thatfor laser pulses of a few hundred picosecond with 4 mJ per laser beam issufficient enough to cause tissue or skin micro-injury through laserinduced optical breakdown (LIOB) or melanin assistant optical breakdown.The subsequent collagen remodeling stimulated by such micro-injury willresult in skin rejuvenation. The current microchip laser is capable togenerate more than 40 mJ 300 ps laser pulses with wavelength of 1064 nm.Therefore, the output energy from the microchip laser can be split intofor example, 10 micro-beams although other numbers of micro-beams arepossible. Each micro-beam will have more than 4 mJ which is sufficientfor effective skin treatment. Each of the micro-beams could be focusedby focusing optics to generate 10 micro-dots.

Skin treatment usually requires irradiation of a two-dimensional skinarea. There is a number of approaches to implement two dimensionalmicro-beam pattern, for example, splitting the microchip laser beam intoa one-dimensional array of micro-beams and manually sliding theone-dimensional array of micro-beams over the skin. Another approach isuse of scanning system to scan the array of micro-beams in one or twodirection/axes. Use of micro-beams or fractional beams with scanningmirrors or other scanning means supports fractional skin treatment.

FIG. 6 is an example of a handpiece for fractional skin treatment. Forexample, the exciting Alexandrite laser could be located in a cabinetand as disclosed in the U.S. Pat. No. 9,722,392 to the same assignee andinventor and incorporated herein in its entirety, the Alexandrite pumplaser beam schematically shown by arrow 606 could be conducted by afiber optics connection to a seed microchip laser 610 located inhandpiece body 604 configured to be applied to the skin. Handpiece body604 could include a high energy seed microchip laser 610 identical tothe described above microchip lasers and a unit of scanning mirrors 614or a polygon spinner or other laser beam scanning means supporting laserbeam 120 scanning in one or two directions or axes (X, Y). This wouldfacilitate implementation of fractional skin treatment. The whole systemof seed microchip laser 610 and scanning mirrors 614 could be smallenough to be packed into handpiece 604. Such handpiece can generatepicosecond laser allowing for fractional treatment for skinrejuvenation.

An optional Second or higher Harmonic Generator 304 could be located inhandpiece body 604. Microchip laser 610 emits a beam with wavelength of1064 nm. When additional to 1064 nm wavelength is required, SecondHarmonic Generator 304 could.be introduced into microchip laser beampath to generate an additional laser light wavelength. Generally, otherwavelength frequency multiplying devices could be arranged on a turretand used when required.

For skin treatment, as illustrated in FIG. 7, the caregiver or usercould manually slide handpiece 604 with one-dimensional (1-D) beamsplitter, for example, a holographic 1-D beamsplitter or scanner overthe treated skin area forming a fractionated scanning system. In courseof the sliding movement, microchip seed laser 610 generates picosecondlaser pulses forming a 1-D fractionated micro-dot 704 line.

Manual movement of handpiece in a direction perpendicular to 1-Dfractionated micro-dot line as shown by arrow 708 generates a 2-Dfractional beam pattern 712. The fractional treated skin area coveragecan be changed by varying the number of fractionated micro-dot 704 in a1-D line and movement speed of handpiece 604. FIG. 7 is an example of arelatively sparse located fractionated micro-dot 704 in a 1-D line.Handpiece 604 movement speed 708 is higher than the same handpiecemovement speed 808 (FIG. 8). Accordingly, a denser 2-D pattern 812 offractionated micro-dots 704 is generated.

In a further example illustrated in FIG. 9 a handpiece for fractionalskin treatment is shown. Generation of a fractionated beam pattern isproduced by a combination of a pair of galvanometer mirrors 904 and 908that project or scan laser beam 120 onto a lens array 912. Lens array912 splits laser beam 120 into a plurality of microbeams 916 which couldalso be fractionated microbeams. Mirror 920 could be used to separateadditional wavelength generated by Second or higher Harmonic generator304 could be located in harmonic generators. The coating of mirror 920is formed accordingly to the desired wavelength separation. Theunconverted infrared light 120 could be directed and absorbed in a laserlight beam dump 924 while the harmonics could be delivered to thetreated skin segment containing a combination of skin disorders. Laserlight beam dump 924 could be designed to effectively dissipate theunconverted infrared energy without getting damaged or causing a rise intemperature of other handpiece 900 components. Passive and activecooling mechanisms can be used as need to remove heat from the laserlight beam dump 924.

The example below provides some operational parameters of a typicalhandpiece used for skin disorders treatment. Seed laser 610 energy couldbe 40 mJ or more. The system is such designed that energy for eachmicrobeam is up to 4 mJ at 1064 nm and 2 mJ at 532 nm.

Such seed laser energy is high enough so that each laser beam from theseed laser can cover at least 9 lenslets to generate 9 micro-dots.Galvanometer mirror pair 904 and 908 scans the laser beam nine times toform a 2-D pattern and cover at least 81 lenslets. Assuming thatmicrochip laser operates at a frequency of 20 Hz, each scan will take0.45 second ( 9/20) or the treatment can be operated up to 2.2 Hz.

It will be appreciated by persons skilled in the art that the presentdisclosure is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the microchip laser andhandpiece includes both combinations and sub-combinations of variousfeatures described hereinabove as well as modifications and variationsthereof which would occur to a person skilled in the art upon readingthe foregoing description and which are not in the prior art.

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What is claimed is:
 1. A microchip laser handpiece, comprising: ahandpiece body accommodating: a microchip laser located in handpiecebody, which is configured to be applied to skin; a fiber opticsconnection to a pump laser; and a fractionated scanning systemconfigured to breakdown a solid beam emitted by the microchip laser andform array of microbeam across a segment of skin; wherein the microchiplaser generates high power picosecond short pulses of energy.
 2. Themicrochip laser handpiece of claim 1, wherein the handpiece body isadapted to slide over the skin.
 3. The microchip laser handpiece ofclaim 1, wherein the fractionated scanning system comprises of a pair ofmirrors.
 4. The microchip laser handpiece of claim 1, wherein thehandpiece body further comprises a lens array configured to generate themicrobeam array from the solid beam emitted by the microchip laser. 5.The microchip laser handpiece of claim 4, wherein the lens arraycomprises a plurality of lenslets and each lenslet receives up to 4 mJat 1064 nm and 2 mJ at 532 nm.
 6. The microchip laser handpiece of claim1, further comprising a holographic 1-D beamsplitter configured togenerate 1-D fractionated micro-dot line.
 7. The microchip laserhandpiece of claim 6, wherein a 2-D fractional beam pattern is generatedwhen the handpiece is moved in a direction perpendicular to a 1-Dfractionated micro-dot line.
 8. The microchip laser handpiece of claim1, wherein the handpiece body contains a second harmonic generator togenerate an additional laser light wavelength.
 9. The microchip laserhandpiece of claim 1, wherein a handpiece body sliding speed sets atreated skin area by laser beam coverage.